Two more planets discovered beyond our solar system

San Francisco State University-based planet search has found nine of 12
extrasolar planets detected since 1995

SAN FRANCISCO, CA, September 24, 1998 -- Deploying the massive Keck
telescope in Hawaii in a new planet search, a team of astronomers has
detected two planets orbiting Sun-like stars, bringing to 12 the number of
distant worlds discovered beyond our solar system.

One of the new discoveries, a Jupiter-sized sphere that most likely appears
deep blue-violet, barely skims the outer reaches of its yellow star, passing
25 times closer to the star than the Earth's orbit of the Sun, and nine time
closer than Mercury's path around the Sun. Its close orbit allows it to
circle its star about every three days. In contrast, the other new planet
has a more Earth-like orbit. Its average distance from its star is nearly
the same as the Earth-Sun distance, the first planet discovered with such a
familiar distance. A year on this planet is 437 days.

"We had discovered planets that orbit much closer and much farther from
their stars than the Earth-Sun distance," said Geoffrey Marcy, University
Distinguished Professor of Science at San Francisco State University who,
along with Paul Butler of the Anglo-American Observatory, has discovered
nine of the dozen planets so far detected.

"We wondered if nature rarely puts planets at one Earth-Sun distance," Marcy
continued. "Now we know that such planets are not rare." Marcy also holds a
post as adjunct professor of astronomy at UC Berkeley.

A report on the planet with the small orbit (around star HD187123) has been
accepted by Publications of the Astronomical Society of the Pacific. The
paper on the planet with the more Earth-like orbit (around star HD210277)
will be submitted to the Astrophysical Journal Letters. Co-authors with
Marcy and Butler on both papers, and colleagues in the SF State-based
discovery team, are Steve Vogt, professor of astronomy at the University of
California, Santa Cruz, who developed the spectrometer needed for planet
detection; Debra Fischer, post-doctoral researcher with Marcy at SF State;
and Kevin Apps, an undergraduate at the University of Sussex.

Apps, a sophomore in physics and astrophysics at Sussex and an amateur
astronomer since the age of seven, is intensely interested in the likelihood
of planets around Sun-like stars. In 1997, he e-mailed Marcy and Butler,
asking if he could see their list of candidate stars in the new planet
search they were launching at the Keck Observatory in Mauna Kea, the world's
largest telescope for optical and infrared astronomy. Upon analyzing the
stars' temperature, luminosity, composition and other features using new
satellite data available on the Internet, Apps discovered that 30 of the
stars were actually not good candidates, and he offered to supply a list of
30 "solar ringers," as he calls them, in their place.

To his surprise, Marcy and Butler agreed to substitute 30 candidate stars
with Apps' 30 solar ringers. One of the newly discovered planets orbits a
star -- HD187123 -- from Apps' list.

"I don't think I can put into words how I feel about Geoff and Paul finding
a planet around one of my suggested targets," says Apps.

Marcy is quite impressed with the young amateur. "He used the latest
satellite data, sifted out the stars that would have the best likelihood of
harboring planets. He shows a fierce interest in this research. It's great
to have him as a colleague."

The two discoveries are among 430 candidates in the new planet search using
the Keck Observatory. The observations were made over 12 nights during the
last nine months, under the auspices of NASA and the University of
California.

Marcy expects to discover "something like" two dozen Jupiter-sized planets
orbiting stars within one Earth-Sun distance. "That should happen within the
next three years if the law of averages applies," he says.

But a second goal of the planet search is to discover Jupiters much farther
out from their stars -- "like five Earth-Sun distances: the signposts of solar
systems like ours," Marcy adds. "Make no mistake about it," he says. "What
we're all about is discovering (planets) where evolution might have gotten a
toehold. Jupiter-sized planets at a greater distance from their star would
suggest a solar system that could host a rocky Earth-like planet. And if it
should turn out that out of more than 400 stars, none has a Jupiter orbiting
at five Earth-Sun distances, that would be a frightening reality. It might
be the first sign that Earth is truly unusual and so life may be rare."

The planets were discovered by detecting a characteristic wobble in the
motion of the star, a wobble caused by the gravitational effect of the
planet orbiting the star. The detection was made using the HIRES
spectrometer built by Steven Vogt and deployed on the Keck telescope.

HD 187123, the star with the close orbiting planet, is a near twin of the
Sun. This star is 154 light years (48 parsecs) away in the constellation
Cygnus (the Swan). The star has the same size, mass, temperature and
luminosity as the Sun, but is richer in heavy elements such as iron. Almost
all planets found to date orbit stars that are at least as rich in heavy
elements as the Sun. This trend toward heavy elements, Marcy says, may be a
clue about how planets form.

The planet is closer to its host star than any planet found before. It
orbits only 0.042 AU away from its sun. (An AU is the Earth-Sun distance).
Indeed, it orbits only four stellar diameters from the surface of the star
HD187123. Its period is 3.097 days.

HD210277, the star with the planet that has the Earth-like orbit, is slightly
bigger than the Sun. It is 68 light years (21 parsecs) away, in the direction
of the constellation Aquarius. The planet has an average orbital distance
barely greater (15 percent) than that of the Earth's. Until now, the
extrasolar planet that had been closest to an orbit the size of Earth's was
16 Cygni B, with an average distance 70 percent greater than Earth's. The
planet is about the size of Jupiter.